Hi Bogie, i would just like to disscuss with you my situation with flow benches and see what you have to say about them. I spent my weekend about a hour or two drive away from my hometown, where someone has a nice small shop and has a superflow 600 flow bench. We have had flow our small and big block chevy heads before and they flowed excellent, to the tune of 240@.500 CFM/180@.600 CFM SBC, and 295@.600/230@.800 lift BBC, and both with more low-lift flow than about any aftermarket head ive looked at. 

Anyway this weekend he flowed a set of heads that I worked on that were from a 401 AMC, anyway, they turned out horrible they fell off @ .450 at around 235 CFM. Now he says that it was our fault that the flow dropped off, he informed us that chucking the valves in a drill and carefully smoothing the top of the seat angle actually hurt the head flow, and also us blending the sharp line on the short side was also detrimental to flow.  He said that we should of put in a larger valve, there is a 2.02 in the head now and a 2.08 can be made to fit, but i responded to that on how bad the shrouding would be since the valve would pretty much hit the com chamber wall

Now i just wanted to ask you about this, can his theories be correct? i see that they flow more air, but when he gets so far away from mainstream ideas i believe he isnt doing the best work, hasnt there been a lot of back to back flow testing done by more educated people than himself and I that has never showed a sharp line on the valve and on the short side to be beneficial? i can imaqine for a mild motor that possibly a sharp line on the short side benefit fuel shearing but, on a flow bench wouldnt this represent a lack of streamlining into the seat that a chevy port wouldnt like

Another question i have to you is how true is the statement, the more flow the better, of course more flow at peak lift will make more peak horsepower probably but what about across the mid range, CHP Impersonator II article really opened my eyes, from swapping 170cc runner vortecs to 180cc AFR heads they lost torque at every point below 4000 RPM's, for a mild cammed 406 this seems important, of course something like 30+ horsepower was gained but something 30+ ft lbs was lost, and this was the smallest runner size that AFR makes! it makes me think that aftermarket heads are more obselete than people think, especially for a dual purpose or street car, street cars arent going to have a lot of duration, lift, low gears, high stall converters, ect. trends would say if you put those AFR heads on a 350 (everything else equal), then you would lose torque below something like 4500 RPM's and so on, so what if you put a 220 CC runner with a 2.08/1.65 valve on a fairly mild 350, would be any better than a set of ported closed chamber production 327 heads? what makes these heads lose so much low end torque, is it low lift efficiency? or a plain loss of velocity, also how do you compare velocity of heads with flow numbers, CFM per CC of runner volume? also what are some other testing that can be done using a flowbench other than shear mass flow, i know that velocity probing is used to check the velocity gradient across the port and see where metal needs to be moved, but what other comparisons can be made by using flow numbers, because the plain flow numbers to me seem to be more useless as i get more experience on a flow bench

P.S. to someone like me would a flowbench be beneficial? i have been considering making one for a while now, i dont have the scratch to get a superflow bench, but i thought if i really tried i could get a fairly accurate homemade one, if you dont believe in homemade benches, is there a fairly good budget minded bench on the market? do you have any info on this? also anything you have to ad about flowbenches, porting, and anything induction related is welcome

WOW, you’re into questions about the art perhaps even more than the science of porting. If you read the books by TCIP on the subject of ports the first thing they say "is that they don't use a numeric controlled machine" to mill the ports, they do them the old fashion way by hand with a flow bench. They further state the reasoning for this is that an NC program fixes the configuration and they have discovered that they keep making new discoveries that lead to continuous improvements. This seems to be true over the long period of time that folks have been taking grinders to ports.

Let me say that Racers are pretty fickle people, they abandon things and people that don’t work for them. So one must consider that this fellow is doing something right even if at a distance from the mainstream thoughts on this subject. There is something to be said about not using a velocity probe as simply placing it into the air stream upsets the flow and disturbs the measurable result. This gets into the old scientific argument that the very act of observing a system upsets that system and what you “see” is not the natural system. However, I like to use velocity probes but do appriciate the problems they introduce and understand the position of guys that rather read gross flow instead of local flows. Yes the aftermarket tends to give up low lift flow in favor of mid to high lift flows. This works for a competition engine where lifts tend to be .5 inch or more but a “warmed up” street engine geared to turn low revs at cruise wouldn’t care for this approach as it reduces low and mid RPM torque and pushes both the torque and power peaks up the rev range. Which is OK if you have the gears to sustain the revs. Otherewise the engine will be slow as it has to wind its way to the torque peak, especially in higher gears or overdrive. So to a large extent the intended purpose of the engine will dictate how you go at the ports. This is to say that the ports, the cam and compression all need an agreement  that supports the vehicle weight, aero drag ratio, gearing and unique track or competition qualities. In-so-far as wet flow and atomization are concerned, in many ways these things take care of themselves within a competition engine where high operating speeds result in extremely turbulent gas flows within the ports and this tends to keep the mixture well homogenized. As the RPM levels drop and port velocity slows the flows become more laminar and centrifugal force may throw fuel out of the mixture. At this point understanding wet flow characteristics become important as now the port needs to be designed to remix the fuel and air streams at some point ahead of or within the combustion chamber to achieve proper atomization prior to ignition. At least this is true of carbureted or TBI engines. Fuel injected engines where the fuel is introduced at relatively high pressure either behind the valve or directly into the combustion chamber don’t have the same problem of maintaining long distance atomization within the mixture. But much care has to go into placing the fuel stream relative to the air stream to achieve proper atomization with these injection systems.

Some things that work on one engine don't necessarily work on another. If you have a copy of David Vizard's book "How to Build & Modify Chevrolet Small-Block V-8 Cylinder Heads" he takes you through the pretty general stuff that's applicable to most anybody's heads. His writing is actually well founded for improving the street engine that also sees some competition. But it really doesn't cover the discoveries and secrets of building competition heads. He does cover building your own flow bench very well. My homemade bench of many years ago was quite similar except it used a furnace fan as the vacuum source. Cranked all the way up this cleared the area of small children, dogs and cats, pulled the carpet off the floor, laces out of your shoes, stuff like that. Of course in reality you have to adjust vacuum, thus flow, to simulate conditions at various lifts. The big problem is that it’s difficult to use a fan to duplicate the real dynamics of gas flow within a port being subjected to variable suction which is dependent on piston position and velocity in the bore, reversion effects caused by exhaust pulse waves and waves generated by closing intake valves, or the effects of valve opening all of which which cause all kinds of pressure pulses going up and down the intake tract. Generally low lift flows are also high pressure low speed flows dictated by the ram effect as flow velocity is converts to inertial mass. However this switches quickly where mid and upper cam lift flows tend to become high speed low pressure events. These variable flow characteristics prefer different shapes within the port and arond the valve. Of course we're subject to finding the compromise shape that offers the best solution obtainable for either case. At low lifts, upon valve opening the piston speed is slow as it’s going around TDC. The previous valve open cycle ended with a high speed low pressure flow that transitioned to a low speed high pressure flow as the valve closed. This happens because inertia tends to keep the flow pouring into the valve pocket where velocity falls off and pressure builds. This also sends a shock wave back up the port. Clever designs catch this wave as it reflects back into the port just as the valve reopens for the next cycle, this adds some over boost or natural supercharge to the mixture. However, when the wave is out of time with engine events it will conspire to reduce cylinder filling. When the valve reopens, this high pressure mixture starts to enter the cylinder even though the piston is hardly moving. Being a low speed high pressure flow the shape of the port and the backside of the valve don’t have too much influence yet except that a smooth backside to the valve or of the port wall causes the fuel and air molecules to stick and form a sluggish boundary layer. A good example of this is the slow speed that rainwater has as it crosses your windshield, this shows the airstream adjacent to the surface is moving very slowly compared to the speed a few inches above that surface. This surface air is moving much more slowly because of molecular adhesion between it the adjacent surface. Inside a pipe (port) this slow moving air or fuel mixture makes the pipe seem smaller to the passing gas flow. In the case of an airplane it adds weight and increases drag. That’s why if you look closely at a jet airliner you will see flush riveting everywhere except at the tail, here you will see headed rivets to roughen the surface. This is used break up the adhesive qualities of the passing air so it will peel off the skin. Otherwise a 747 would be dragging a layer of sluggish air 10 feet deep all around the tail. You need the same thing inside a port especially where the sections are divergent (opening away from each other).  Getting back to piston movement and air flow, by the time the valve is at mid lift the piston is moving very quickly down the bore and gas velocities are becoming quite high. At this point port pressure is falling and flow is very port shape dependent as inertia forces everything toward the outside of turns. Here clever shaping to induce small but extremely low pressure eddies can be used to force the mainstream to make turns it otherwise wouldn’t. Some of these features such as an abrupt “Kamm” cut on the short side turn or a lip on the backside of the valve help make the apparent size of the port seem larger to the flow than the more intuitive design of smooth streamline shapes would. Once the piston passes half way down its stroke it begins to quickly slow, but the gas velocity it imparted to the incoming mixture is so high that the flow keeps coming even though the piston has slowed and even reversed direction past BDC all while the valve is closing. In a competition engine there is significant flow well into the compression phase before the valve must be shut to trap the charge. Which emphasizes the need to shape for low speed flow as the result of some compromise on the high speed flow. This is a way of saying you need a compromise that makes the best of both low and high speed flows but will not be perfect for either. Again the use of the engine will dictate which way the compromise favors. A full out competition engine with a very high lift cam will lean toward making optimum use of the extreme lift. Of course pressure continues to build behind the closed valve because of the inertia effect from the intake flow and the process repeats as the valve reopens. At low speed, of course, these inertia effects are not present and the engine 9especially with a long duration, high  lift cam) reverse pumps the intake charge back out the carb. This results in the ragged idle of a hot cam. Now appriciate that this is a simplification as I haven’t gotten seriously into wave effects which can be significant for or against flow. Lingenfelter, Morrison, Holley, TPIS and others have good books out there on the subject of porting. Type "Engine Porting" into your search engine and stand back, whip out your credit card and start buying books.

Now general theory suggests that opening the valve beyond a fourth of its diameter doesn't improve flow to any great extent. If you review the published data on head flow you will see an indication of truth to this in that at lifts higher than .25 the valve diameter show a very marked decrease in the rate of flow improvement. However, if your building a competition engine, these small improvements at .6 to .8 inch lift for a valve around 2 inches in diameter can provide the difference between winning and loosing. So while theory correctly predicts the slowing the increase in the rate flow, it by no means suggests that a competitive racer should not go there.

Some engines like 30 degree intake seats and some don't care. Again Vizard discusses this in his book, or aims you at another one of his books that does. Way back in my FoMoCo days, the Ford FE (332-428) liked 30 degree seats, though the Tunnel Port 427 seemed immune to them vis-à-vis a 45 degree seat. The Chevy Rat and the MoPar Hemi didn't seem to care either way. The AMC engine has a pretty tight turn into the pocket, similar to the FE Ford and probably would like a 30 degree seat.

Valves in different engines and with differently ported heads respond differently to back cutting. Some like the back side to be smooth and others don't. This gets back into the discussion of energizing the boundry layer flow to get to let go of the port wall and the backside of the valve. The same can be said about the shape of the port as it blends toward the valve seat or as the bottom of the runner comes around the tight turn into the pocket. Some ports like this area to be smooth and diverging to the seat such as those of Small Block Chevy and MoPar engines. Others like a smooth venturi shape just ahead of the seat. Some respond well to what could be thought of as a sharp edged venturi ahead of the seat. The smooth flow around the valve that is portrayed in Smoky Yunick's book while very pretty, doesn't exist because in the real world the flow is not symmetrical around the valve and in the case of a 2 valve wedge would be fatal to power output as it would foster a tumble port which 2 valve wedge chambers do not like.

You can use various shapes in the port to pull air around or put it where you want it. Cutting off the bottom of the port as it joins the pocket on the short side radius making a "Kamm" style termination can be effective in pulling the airflow around this corner. Some people also dimple this area like a Golf Ball’s surface for the same effect without causing fuel to puddle ahead of the Kamm spoiler shape. These create a very tight low pressure local swirl that pulls the passing mixture tightly around the turn. An airplane example from back in the early days of the F-111 test flight program was that the aircraft was incapable of hitting its top dash speed requirement. An engineer at Convair got the idea of actually cutting the end of the fuselage off and putting a kick up spoiler on it as Dr. Kamm's experiments suggested was good to terminate the flow and recover forward momentum from the passing airflow. While this created more drag than a smoothly blended shape between the engines, it provided more “thrust” than drag and helped push the airplane forward. The rest, as is said; "Is History". 

So the lesson in all this is that this is less an area of uniformity where one size fits all and more an area of continued experimentation. That said, his statement of his heads generating 80 more horsepower than yours because he has better max lift flow but less low lift flow would be true for the right cam and RPM leading to a “more” useful port velocity combination. Obviously, if you used a cam with .45 inch lift with his heads the superior ultra high lift flow would be of no consequence. The reverse would also be true, in that your porting would peter out in these high lifts so a cam of .5 inch or more would not be effective. All this assumes that the duration remained the same for the lower or higher lift cam. At some point the port or the valve reaches all the flow it can pass in a given moment. Holding everything else steady, the only improvement is more time with the valve open and that's controlled by cam duration in this case. Certainly lobe shape also plays in this but for argument I'm considering them to be the same.

He's right about the valve flow on the cylinder wall side for a two valve wedge. For the most part there is little to no flow on that side of the valve adjacent to the cylinder wall and you don't want to encourage flow from there as it will oppose the swirl pattern and reduce overall flow. Now 2 valve hemi chambers and 4 valve pent chambers, or engines with blowers exhibit different flow patterns largely grouped into what's called "Tumble Ports" However, if you force this to occur on a 2 valve naturally aspirated wedge power goes out the window and fuel consumption goes up indicating a loss of efficiency. The suggested larger valve will help top end power by increasing the area of flow which also tends to reduce top end port Mach numbers. You don't want to drive the flow into local supersonic as the shock wave is as solid to flow as a piece of metal obstructing the passage. How you use the engine should be your guide. If you can keep the revs high, then big high lift flow is beneficial to you, if the engine has to grunt its way up from low RPMs, then you need to design around more torque which usually means smaller ports and less cam timing and lift. My own approach to ports is to get the most flow with the smallest volume necessary to get the job done. So I compute the theoretical max volume needed to fill the cylinder. Then work to achieve that flow with the smallest port that keeps max velocity at or below .5 or .6 Mach. This usually leads to unusual shapes, raising the port and sometimes filling the lower sections. But all this is variable as to what it takes to get the engine to perform for the task at hand. Sometimes big flows just kill the engine even at high revs, you just have to cut and try if you're on the competitive edge. If you want a hot street engine that occasionally races then a set of machine ported heads are the most bang for the buck you're likely to find. If you’re a competitive racer, then you stand up against the line of known knowledge and experiment on the other side of the line.

The subject of 11/32 valve stems against 3/8s in my experience is highly overrated. The 1/32 less diameter just doesn’t buy much flow and reduces available stem strength. This is especially true of hollow stem valves. Having had valves fail, I fall on the side of greater reliability against a couple CFMs of flow as the cost of a failed valve is high, not only do you become a DNF but your engine becomes several hundred pounds of junk and those expensive custom heads are almost always a total loss.

I can't really comment on his ideas and theories other than to say that "Mainstream Ideas" as you read in books and articles tend constitute the status quo. The guys who step over the edge are the guys that discover things that make the new status quo or find themselves up a blind alley. Either way experimentation is what's required to separate what works from what doesn't. I say that 2 grand for a set of heads is an expensive way to discover things, but to a large extent it's part of the admission price to being a competitive racer. That being said it won't take you many heads to pay for a decent flow bench whether homemade of a Superflow. You'd choke over the pile of junk heads I've made over the years, which is why I started making silicon patterns of stock ports then casing them in plastic and modifying the plastic ports for the flow bench, or making acrylic models of port's I'd like to see, it's a lot less expensive than wrecking heads with ideas that don't work. And in the case of long out of production engines such as the AMC, you’re not ruining things that are increasingly rare.

Bogie

I think a question that is fitting right now is, Are You Human? it does make me think when i havent seen a question that you couldnt answer on this message board

Thanks for you comments on my questions. I can see common sense and a flow bench dont mix. Once again though after reading your material i have stirred up a few more questions

I realize that the fuel will do a better job of staying in suspension with high RPM engines but what about checking swirl? do you use a swirl meter? how is it possible to change the angle at which it enters (seem to remember reading something on this but am a little cloudy) and how do you diagnose a flow loss due to a swirl reversal? also dont wet flow benches better help understand what is going on in the chamber for burn patterns and such? and if they do what are some things that one should look for that are "bad" for the burn quality and other things. What kinda of shaping involves a swirl port vs a tumble port and how do you diagnose when you have generated too much tumble in a swirl designed port?

your topic on layered flow made me think a little about some valves that i have seen that have been smooth, dosome ports prefer this since this effect wont be as severe, or should you not use smooth valves and if you get a valve with a smooth surface what could be done to roughen it enough to make the air more turbulent

this sounds like a stupid question but is the major difference in making the port diverge to the seat or making a venturi, i always thought that a venturi shape was best for a small block chevy just before the seat, is this wrong? do you know if the common SBC port likes a sharp line on the short side before the seats or is this just to other styles of ports

i realize that most of the flow at high lift on a head like the SBC is across the valve because there is a chamber wall there but i always got the impression that if no unshrouding was done power would be lost by putting the 2.02 valve into a closed chamber head, are they speaking of low end torque? from a reduction of low lift flow only? does chamber wall shrouding make any difference to a high RPM engine, high lift, low geared engine? or is shear valve area more important?

the golf ball surface on the short side of the port interested me, can you give me a little details for actually phsyically doing this procedure to a small block chevy? like what tool can be used, how deep and what diamter should the dimples be and where should they be placed

On these AMC heads we are now using a 39* angle with a 30* backcut on the valve and 60* buttom cut and a 24* topcut on the seat, i see that you believe that a 30 will work better with the tighter turn, what can be done in the port to make this turn less abrupt? or do you believe that a 39* angle is flat enough that it will be fine

what are some conditions where too much flow will a kill a engine's output everywhere including the high RPM's, im afraid that even though this family friend of ours who is much smarter about this subject than I thought might be doing this as really he shoots for a flow number and ignores the lift to get there and ignores the volume also and usually goes through a lot of his ports and epoxies them with few problems, he doesnt often has his engines dyno'ed either, so i can just try to point out the "good" and the "bad" of his theories that he routinely tells me a little better

Even though we didnt discuss it earlier, after looking at the flow numbers for the 401 AMC heads it made me think about the E/I Ratio. When is there too much exhaust flow for the intake flow and what negative or positive effects does this have on output, the current average E/I Ratio flow from .1-.5 is around 75% (without a pipe and with a radiused entry into the intake port), is it safe to say that this is too high and trying to achieve more intake flow and leaving the exhaust port alone is the right route to take?

One more thing, you say that flowbench is for comparison reasons only, but on what aspects should you compare two different heads, average flow over a lift curve or just flow at peak lift, flow per sq inch of valve area? flow per cc of runner volume? this question is derived from me thinking about how can you quote a horsepower increase by increasing flow a certain amount at the cam's peak lift point, would there be too many variances to quote a somewhat accurate horsepower increase, or is a engine just that much of a air pump

Thanks again

We put the AMC heads back on the flowbench yesterday, at .300 they picked up 12 CFM without changing the port volume a CC. but the flow @ .200, .400, and .500 were all the same, and the flow was substantially less at .100, but the flow was also 6 cfm more @ .600. Thinking about what you said, that a AMC has a fairly tight short side turn, and basically just screwing around, i dimpled the short side as far back as i could from the bowl, and without a answer from you, made the surface very similiar to a golf ball, in the size and spacing of the dimples, I made more dimples on the cylinder centerline side of the port continuing a bias theory, and i also made many smaller, much, much closer spaced dimples on the long side of the port starting at the buttom of the 60* cut and working about a quarter of a inch back, in theory trying to break up the lazy boundry layer of air, but i also blended the buttom the 60* cut in the port so there was no sharp line, all the way around,is this the right or wrong thing to do? but we didnt blend the top of the 30* backcut on the valve in, so there was somewhat of a line on the backside of the valve, but it was very smooth to the touch so we didnt worry about it.

After all of this the heads still only 241 CFM @ .600, but this was on a 4 inch bore, so it may or not be changing the numbers, since the bore on the engine is around 4.2. The owner of the flow bench instructed me to grind on the pushrod bump in the port in my quest for more flow, but said that it would only start picking up @ .500 and above and we are flowing about as much air as we can for a cam this small (lift is <.500). The port's current dimension at the pushrod constraint is 2.12 tall by .95 wide, do you believe that this should be increased? I was always lead to believe that in a lot of cases it should be left alone, which we did, but what do you have to say about this?

thank you very much and im sorry for loading you down with so many questions at once, but as you can see it really bothers me to see my questions go unanswered and you are the one of the only people that will answer these type of questions for me, thanks

I've been travelling this week and getting time to sit down and write has been very difficult. I'll try to get some words put together this week end.

Bogie

I'm going to repeat your questions with my answers in bolded type.

I think a question that is fitting right now is, Are You Human? it does make me think when i havent seen a question that you couldnt answer on this message board. I think of myself as a renaissance man, my wife thinks I’m Butt Head.

Thanks for you comments on my questions and it really made me realize that i once again acted like I knew it all. I can see common sense and a flow bench dont mix. Once again though after reading your material i have stirred up a few more questions

I realize that the fuel will do a better job of staying in suspension with high RPM engines but what about checking swirl? do you use a swirl meter? how is it possible to change the angle at which it enters (seem to remember reading something on this but am a little cloudy) and how do you diagnose a flow loss due to a flow reversal? also dont wet flow benches better help understand what is going on in the chamber for burn patterns and such? and if they do what are some things that one should look for that are "bad" for the burn quality and other things.   Measuring swirl, tumble and wet flow can be done by measurement (quantitative) or by observation (qualitative).  For quantitative measurement there are two predominate measures the first being swirl meters the other Pitot tubes. There are commercial swirl meters and Pitot tubes available for flow benches see the URL  <<< http://www.performancetrends.com/pfa.htmhttp://www.performancetrends.com/pfa.htm >>>. Basically swirl meters are a propeller that turns a generator. They are placed in what would be thought of as the upper cylinder portion of a flow bench just under the head being tested. Their read out is pretty gross as they measure what ever the cumulative effect is rather than local flow. They can be used horizontally to measure swirl flow or mounted vertically to measure tumble. You get both flows with a 2 valve wedge but you want swirl to be the predominate flow. The air flow spins the propeller which being connected to a small (toy) generator produces a voltage that is proportional to RPM; i.e. more voltage equals more swirl or tumble. Flow loss due to reversed swirl would be read as reduced RPM of this gadget. Another technique is the Pitot tube (“Pitot” is a guy’s name hence in caps) this is placed in the air stream and the resultant pressure forces correlated to pressure differential or air speed depending on whose system (home made included) you’re using. See these URLs for a technical description of Pitot tubes <<< http://www.grc.nasa.gov/WWW/K-12/airplane/pitot.html >>> and <<< http://www.efunda.com/designstandards/sensors/pitot_tubes/pitot_tubes_theory.cfm >>>. But remember both of these techniques are invasive so they have an affect on the flow you’re measuring. That doesn’t necessarily invalidate the results but you need to think about the disturbances these tools can cause.

Wet flow is a visual thing if you have the money the Mondello flow bench with a dye in water solution can be used <<< http://www.mondello.com/Pages/Catalog/mondelloCFM.htm >>>. If you have a home made flow bench with a shop vac as the power source you can also flow a water dye solution. Don’t flow gasoline or other flammable liquid unless your life insurance is paid up. I often use a little shot of model railroad paint, this is an extremely fine ground pigment and can be had in either water or petroleum based solvent. Water solvent has obvious safety and health benefits. Another technique I use is a model railroad smoke generator to provide a stream to a very small tube that can be used to observe flow as it enters an acrylic cylinder or in clear plastic port models I make. This allows you to actually see where the flows are going without sticking measuring tubes or propellers down the port.       What kinda of shaping involves a swirl port vs a tumble port and how do you diagnose when you have generated too much tumble in a swirl designed port?  To a large extent a typical production 2 valve engine rather solves that problem. However, exceptions exist the GM Iron Duke 4 with a carburetor manifold and the Ford FE engines come to mind. The Iron Duke is the poster child for understanding that the intake manifold and the port shapes need to work together. In this case the center 2 cylinders are fed on the wrong side of the port wall which slams the incoming mixture into the cylinder wall as a result of how the flow is set up by the manifold. The Ford FE has a similar problem but Ford engineering corrected the orientation of the flow with a “S” bend in the port. If you straighten that bend the engine instantly gives up a 100 horsepower. The Chevy and the AMC naturally have pretty good swirl characteristics, the SBC being better because when compared to AMC’s gompy guide boss it’s apparent how the AMC guide just plugs up flow right where you want it. Of course the opportunity here is that there’s plenty of meat to shape this guide. Basically swirl is enhanced by increasing the port height along the side adjacent to the cylinder wall. You want to continue that shape on the topside turn into the pocket increasing the width between the wall and the guide. Another trick is to drop the bottom of the port floor and slightly widen the lower wall of the port side that favors the center of the cylinder, blending the floor smoothly at the short side radius to form a high side from the wall adjacent to the cylinder wall down to the wall favoring the center of the cylinder. This gives the port a twisted trapezoidal shape that allows the flow on the upper port to sweep across the pocket and out in a swirl along the combustion chamber wall from the intake over the sparkplug and exhaust valve. The shape of the floor into the tight turn radius allows that flow to drop toward the center of the cylinder in the direction of the principle swirl flow. The guide needs to be streamlined as much as the available material allows. The leading edge can be ground to engage as much as of the upper port roof flow as is possible to move it around the side adjacent to the cylinder wall side. The back side of the guide can likewise be shaped in the direction of the flow so its trailing edge favors a direction toward the center of the cylinder as much as the material will allow. Unfortunately most modern heads don’t provide much material here anymore and certainly aluminum heads with press in guides have none. For them, this allows the flow to find its own way which is usually turbulent and inefficient.

your topic on layered flow made me think a little about some valves that i have seen that have been smooth, do some ports prefer this since this effect wont be as severe, or should you not use smooth valves and if you get a valve with a smooth surface what could be done to roughen it enough to make the air more turbulent. Once the gross flow has been set up in the port, then you need to work the idiosyncrasies of the valve and seat. This is mostly cut and try as the flows here are very dependent upon the shapes and flows ahead of this point. Some ports like a smooth valve and seat transition, others like a little abruptness through here. For the valve most texts recommend a 30 degree back cut to remove the seat lip and blend it into the backside. Others like the lip or at least some portion there-of to remain to help trip the boundary layer. Some folks do the 30 degree back cut and then cut a shallow ditch on the backside where the inside edge of the lip used to be. Overall the backside of the valve can be roughened up sand paper or a stone. The ridges should be circumferential with the diameter so they are what’s called normal (at 90 degrees) to the flow direction.  Your just going to have to play with these shapes to see which is the most responsive.

this sounds like a stupid question but is the major difference in making the port diverge to the seat or making a venturi, i always thought that a venturi shape was best for a small block chevy just before the seat, is this wrong? do you know if the common SBC port likes a sharp line on the short side before the seats or is this just to other styles of ports. Typically, the short side radius just drops to the seat, as it does on the side adjacent to the cylinder wall. You just don’t want to encourage flow on this side. As the pocket transitions toward the sparkplug side you want to have a small venturi shape as the wall approaches the seat, this should carry around the center of the cylinder side and taper toward and ending where the short side turn blends back into the pocket.  

i realize that most of the flow at high lift on a head like the SBC is across the valve because there is a chamber wall there but i always got the impression that if no unshrouding was done power would be lost by putting the 2.02 valve into a closed chamber head, are they speaking of low end torque? from a reduction of low lift flow only? does chamber wall shrouding make any difference to a high RPM engine, high lift, low geared engine? or is shear valve area more important? The 2.02 or larger valve will improve flow. There are people concerned about shrouding on the cylinder wall side, but you don’t want much if any flow here as it will be counter to the swirl direction.

the golf ball surface on the short side of the port interested me, can you give me a little details for actually phsyically doing this procedure to a small block chevy? like what tool can be used, how deep and what diamter should the dimples be and where should they be placed. I use a Dremel tool with flex shaft with a number 107 engraving ball cutter. When I do this, I usually limit the area to the short side radius from the middle of the port floor toward the wall adjacent to the center of the cylinder but not onto that wall’s surface.

On these AMC heads we are now using a 39* angle with a 30* backcut on the valve and 60* buttom cut and a 24* topcut on the seat, i see that you believe that a 30 will work better with the tighter turn, what can be done in the port to make this turn less abrupt? or do you believe that a 39* angle is flat enough that it will be fine. The 30 degree seat if it works at all seems to really do better on tight turning ports into the pocket and at that with lifts in excess of .5 inch. Unfortunately there’s not much that the porter can do to change these angles. Porting is a material removal process where fundamental changes often require adding material or moving the port which isn’t very practical. Sometimes you can raise the roof by grinding and raise the floor with epoxy and while you may loose port volume the improved streamlining and pocket/valve entry angle can overcome an apparent loss of volume. Epoxy is OK for a competition engine that gets torn down and inspected frequently, but probably doesn’t have the longevity for a street engine.

what are some conditions where too much flow will a kill a engine's output everywhere including the high RPM's, im afraid that even though this family friend of ours who is much smarter about this subject than I thought might be doing this as really he shoots for a flow number and ignores the lift to get there and ignores the volume also and usually goes through a lot of his ports and epoxies them with few problems, he doesnt often has his engines dyno'ed either, so i can just try to point out the "good" and the "bad" of his theories that he routinely tells me a little better. Too much flow of itself doesn’t kill power, it’s too much port volume for the engine’s operating speed. Large ports reduce flow speed throughout the rev range compared to smaller ports. At certain speeds or RPMs the flow could reach a point where inertia effects, or lack there-of, reduce cylinder filling the same as too much cam or carb. This in a theoretical sense is just the nature of the beast since we’re stuck with one size fits all sized ports for conditions from idle to redline. So what you’re doing with the engine and how the driveline is configured becomes all important. A competition engine with a manual gear box and stiff rear gears can be kept in a high rev range which not only demands large ports and valves but can also be operated there. The same engine with an automatic and high ratio rear gears would be difficult to operate at continuously high revs. Being forced to lower RPMs would make the engine lazy and balky to throttle inputs till you could really get it turning. Of course the reverse is true for small ports and valves, such an engine couldn’t get into a rev range to be competitive at the track, but would be pleasant on the street.

Even though we didnt discuss it earlier, after looking at the flow numbers for the 401 AMC heads it made me think about the E/I Ratio. When is there too much exhaust flow for the intake flow and what negative or positive effects does this have on output, the current average E/I Ratio flow from .1-.5 is around 75% (without a pipe and with a radiused entry into the intake port), is it safe to say that this is too high and trying to achieve more intake flow and leaving the exhaust port alone is the right route to take? An exhaust valve sized at 75 percent would be on the high side for a street engine, for a competition engine that is run a lot at WOT, this is probably more realistic given the amount of exhaust flow that needs to be eliminated. Over scavenging could become a problem, but most people either put a restriction in the exhaust or just jet the carb up an live with the lower fuel mileage which could be a problem for long distance, limited fuel quantity races.

Thanks again

i will show you the before and after flow numbers, just mainly for the hell of it and see if you pick anything out

if you could just throw some ideas my way, why the large 12 CFM increase @ .300 and the measurable increase @ .600, but nothing or a decrease everywhere else. After reading your answer to my question about the dimples on the short side mimicking a golf ball surface, i realized that even though i made more, and more pronounced dimples on the cylinder centerline side of the port, that i probably put to many on the cylinder wall side of the port, and possibly could of brought too much flow to the shrouded side of the valve

also if you are to totally discourage flow from the cylinder wall side of the port, what should you do on the seat there, make a more abrupt sharp line? or find what the port likes and do the opposite on that side of the port to try to cut flow there as much as possible?

can you throw me a bone at all, at what a common production small block chevy port would like on the seats? since i dont have a flow bench, YET, im not sure if they would prefer blending of the buttom cut into the bowl, or leaving the sharp line, or blending the top of the backcut into the backside of the valve, or once again leaving this sharp line

are you familiar with a formula that involves taking the area at the port's pushrod restriction and figuring out how much CFM that the port is possible to flow, the owner of the flow bench talked to me and said that a port this size (2.12x.95) can flow 294 CFM and currently our port is flowing 82% of that, yet if we made the port width .100 larger that can jump the flow up to 266 CFM if the efficiency stays the same, is it that simple, that just widening the port at the pushrod constriction will gain you that much flow and that much power? seems a little too good to be true, but its not like i've never been wrong

i will also show you a picture of the port, to see if you can see anything drastically wrong just by a glance, excuse the quality of the photos, im not that good with a digital camera, but if there is anything else you think you can help me with (without giving out too many of your secrets) within the port and need a more in-depth picture of that area i would be glad to take some more snapshots, make any comments that you'd like, i need anything you have to say.

one more question for tonight and im done, do you build performance engines or port heads for a living? im wondering why you have all this high dollar equipment and all of this performance engine experience. What would you prescribe to a 16 year old who plans on majoring in mechanical engineering and dreams about building engines for NHRA Pro Stock one day? lol

Nice pictures, my only comment from seeing them would be to suggest that the guide on the side adjacent to the cylinder wall be opened up at it's base making the guide made more vertical and widening the port's passage on that side.

Bogie 

so you think that the port needs even more bias, is there a clear way to tell how much bias a port would need, and do you usually use more than a norm for the amount of port bias in a SBC

just a little reminder incase you missed it, my previous message was kinda strange in where it got cut off but it did get truncated, so if you missed them, could you please answer my questions in my previous post when you get time, thanks

I caught your previous message an am building a reply.

Within the shape and amount of material available, it's not possible to build as much bias into the port as the engine would like by grinding. I've been trying to find some pictures of the Gurney Westlake Ford SBF heads to show you how it should be done, if you have the resources to make your own head form scratch. These won Indy and many other places on what was otherwise a stock block SBF back in the early 1960s. The intake pretty much drops almost straight down on the intake. The combustion chamber is a carodit (heart) shape pioneered by Sir Harry Ricardo back in the first half of the 20th century. A shape which today has become the latest thing in fastburn combustion chambers. The exhaust rolls out in the stock location of the outside of the head, but comes out as high and as smooth as is possible.

Bogie 

gib

your under 20 y/o

he's 80y/o and made a good sized bus.. of porting and flowing heads.....

I'd  shut up and lessen to all he has to say  and memorize it...  after you know all that he does then start ? the way he flows/ports heads...

I think that he was able to tell you what you did wrong and then helped you by saying what thing would help flow and what is not worth it.. is a big plus..

you ever think that in all his years that he mostlikely has tried the thing you did to the 401 heads...  I'll bet he has....

your lucky to be able to learn from him, use it  before it's gone...

you'll have plenty of years to try and prove his ways wrong after he's gone  but I'd for now  "TAKE IT ALL IN!!!!!!!!!"

may i ask what you are talking about? i didnt think i was being unappreciative or trying to prove him wrong in anything, did i word something wrong that you interpreted the wrong way, ???. If i was i apologize to bogie

no  no  in your first post u talked about the guy you know that flows heads and that he test for different flow points than seem hard for you to fathom...   and doesn't even bother with low lift(off the seat) flow..

I was just saying that if you can spend time with him....  pick his brain...  as it got tons of flow test does and don't in there and is a gold mine   ...  use it before it's gone..... 

you worked over some 401 heads and he told you where you went wrong and what would work better.......

thats a "bin there done that " moment......  he's done it and knows the resulting flow before it hits the flow bench....

those guys have tricks that they pass on only when they know they can't benifit from it no more...

so pick his brain(who ever is the guy with the flow bench u used) cause it's full of knowledge..

oh i thought you were speaking about what i said to bogie, but yes this person who makes a living porting heads well, your right i should respect him, but i need to make sure to pull the good from the garbage. i cant get myself to believe what he does with only flowbench data to back it